Display device

ABSTRACT

A contact resistance in a through-hole with a source or a drain electrode connected to a TFT is decreased, thereby improving the operation efficiency of a display device. 
     In the through-hole, a source portion of the TFT is connected to a source electrode  8 . The source electrode  8  is formed of three layers comprising a barrier metal, an Al alloy  82 , and a cap metal  83 . The barrier metal is divided into a lower layer  81   a  in contact with the semiconductor layer and an upper layer  81   b  in contact with the Al alloy. The lower layer  81   a  of the barrier metal is formed by sputtering, the lower layer  81   a  is heat-treated and, subsequently, an upper layer  81   b  of the base metal, the Al alloy  82 , and the cap metal  83  are formed continuously by sputtering. Since the upper layer  81   b  of the barrier metal in contact with the Al alloy  82  is not oxidized, increase in the contact resistance in the through-hole can be prevented.

CLAIM OF PRIORITY

The present application claims priority from Japanese Patent ApplicationJP 2010-032439 filed on Feb. 17, 2010, the content of which is herebyincorporated by reference into this application.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a display device. The invention moreparticularly relates to an active matrix type display device which isimproved in the response speed or the emission efficiency by decreasingthe contact resistance in a through-hole.

2. Description of the Related Art

In an organic EL display device or a liquid crystal display device,scanning lines are extended in a first direction and arranged in asecond direction. Further, video signal lines are extended in the seconddirection and arranged in the first direction. Areas surrounded by thescanning lines and the video lines define pixels and a thin filmtransistor (TFT) is formed for each of the pixels.

The organic EL display device is configured to control current suppliedto an organic EL layer by a TFT while the liquid crystal display deviceis operated to select signals on images supplied to pixel electrodes.The TFT is formed of a-Si or poly-Si.

In the organic EL display device, since the organic EL layer is drivenby the current, it is necessary to increase the mobility of asemiconductor constituting the TFT. Further, a small-sized liquidcrystal display device is such that a driving circuit is mounted in aliquid crystal display panel. Since high speed operation is necessaryfor the TFT for the driving circuit, it is necessary to increase themobility of the semiconductor. Accordingly, a poly-Si TFT is used in theorganic EL display device or the small-sized liquid crystal displaydevice.

Generally, to form a poly-Si semiconductor layer, an a-Si semiconductorlayer is first formed and then excimer laser is radiated to the a-Sisemiconductor laser to convert a-Si into poly-Si. Installationinvestment is necessary and process control is difficult for theradiation of the excimer laser. In view of this, JP-A-2007-142059 that asemiconductor layer of poly-Si is formed by radiating an a-Sisemiconductor layer not by the excimer laser but by light of a lamp.

SUMMARY OF THE INVENTION

Generally, to form the poly-Si TFT, a semiconductor layer is formedfirst and a gate electrode is formed above the semiconductor layer, witha gate insulation film being sandwiched therebetween. An interlayerinsulation film is then formed above the gate electrode. A sourceelectrode or a drain electrode (hereinafter represented typically by thesource electrode) is formed above the interlayer insulation film. Thesource electrode is in a layer in which the video signal line extends.An inorganic SiN passivation film is formed above the source electrodefor protection of the entire TFT and an organic passivation film isformed above the inorganic SiN passivation film.

The source electrode is connected by way of a through-hole formed in theinterlayer insulation film to a source portion of the semiconductorlayer. An Al alloy is used for the source electrode which is formed in alayer in which the video signal line extends so as to decrease theresistance. However, Al atoms tend to migrate. The Al atoms are diffusedto a semiconductor layer when they are passed through a thermal step oroperated for a long period of time, resulting in the characteristics ofthe TFT changed.

In order to prevent this, a barrier metal such as MoW is formed as anunderlayer for the Al alloy in the source electrode. While the barriermetal is formed by sputtering, the barrier metal in the state assputtered has no sufficient barrier effect for Al. Accordingly, afterthe barrier metal is formed, it is necessary to subject the same to aheat treatment to increase the density of the barrier metal therebyimproving the barrier effect. However, the heat treatment step resultsin a phenomenon of oxidizing the battier metal. When the barrier metalis oxidized, Al is oxidized thereby resulting in a problem of increasingthe contact resistance with respect to the Al alloy.

FIGS. 8 to 12 show a process of forming a poly-Si TFT according to theexistent method described above. In FIG. 8, a first underlayer 2 of SiNis first formed on a substrate 1, and a second underlayer 3 of SiO₂ isformed on the first underlayer 2. They are formed for preventingimpurities contained in the glass substrate 1 from contaminating asemiconductor layer 4. Subsequently, an a-Si film is formed as thesemiconductor layer 4. An excimer layer is radiated to the a-Si film toconvert it into a poly-Si film. Then, the semiconductor layer 4 ispatterned by photolithography.

In FIG. 9, after a gate insulation film 5 is formed on the semiconductor4 layer, ions are injected into the semiconductor 4 layer byimplantation. The conduction type of the channel portion is defined toeither a p-type or n-type by the ion injection. After the ion injection,a heat treatment is applied for the entire substrate 1. This step isperformed for driving atoms injected by ion implantation into thesemiconductor layer 4 and activating them.

Subsequently, a gate metal is formed over the gate insulation film 5 bysputtering, and the gate metal is fabricated by photolithography to forma gate electrode 6. Although not illustrated in FIG. 9, an impurity suchas P or Bo is injected by ion implantation using the gate electrode 6 asa mask to form a drain portion or a source portion in the semiconductorlayer 4. The drain portion or the source portion is in contact with adrain electrode or a source electrode 8.

In FIG. 10, an interlayer insulation film 7 is formed on the gateelectrode 6 by plasma CVD, etc. After the interlayer insulation film 7is formed, a heat treatment is performed for the entire substrate 1 andthe ions injected into the drain portion or the source portion of thesemiconductor layer 4 are driven into the inside and activated.Subsequently, a through-hole is formed in the interlayer insulation film7 and the gate insulation film 5 such that the drain portion or thesource portion of the semiconductor layer 4 can be in contact with thedrain electrode or the source electrode 8.

In FIG. 11, a barrier metal is formed on the interlayer insulation film7 by sputtering. The barrier metal is formed, for example, of MoW. Thebarrier metal can be also formed by high melting point metals typicallyrepresented by Mo, Ti, Ta, Mn, Ru, V, and Co, and compounds or alloysthereof. Since the barrier metal is sputtered also in the through-holein the interlayer insulation film 7, the drain electrode or the sourceelectrode 8 can be in contact with the drain portion or the sourceportion of the semiconductor layer 4.

While the barrier metal serves as a barrier for an Al alloy 82 to besputtered subsequently, the barrier metal does not form a sufficientlydense film only by sputtering. To attain the barrier effect, it isnecessary to subject the sputtered barrier metal to a heat treatment.

The heat treatment is performed, for example, in an N₂ atmosphere afterthe substrate 1 is taken out from a sputtering device into atmosphericair. The surface of the barrier metal is oxidized when the substrate 1is placed under the atmospheric air.

As shown in FIG. 12, an Al alloy 82 used to form the drain electrode orthe source electrode 8 is sputtered over the barrier metal. If thesurface of the barrier metal is oxidized, then this oxidizes Al incontact with the barrier metal to increase the contact resistance in thethrough-hole. If the contact resistance increases, current that allowsan organic El layer to emit light cannot be sufficiently obtained in anorganic EL display device and the switching characteristics aredeteriorated in a liquid crystal display device.

The present invention intends to prevent the increase of the contactresistance in the through-hole.

In accordance with the invention, to overcome the problem describedabove, a source electrode to be connected with the source portion of aTFT is formed with three layers comprising a barrier metal, an Al alloy,and a cap metal. The barrier metal is formed in such a manner as to bedivided into two layers comprising a lower layer in contact with thesource portion of the TFT and an upper layer in contact with the Alalloy.

First, after the lower layer of the barrier metal is formed bysputtering, the substrate is taken out of a chamber and subjected to aheat treatment. The heat treatment is performed for increasing thedensity of the film structure in the lower layer of the barrier metal toprovide the barrier effect. Subsequently, the substrate is again loadedin the vacuum chamber, the upper layer, the Al alloy, and the cap metalof the barrier metal are formed continuously by sputtering.

While the lower layer of the barrier metal is oxidized when taken outinto the atmospheric air, the layer is covered by the upper layer of thebarrier metal sputtered subsequently in vacuum, and the barrier metaland the Al alloy are not in contact with each other. Thus the Al in theAl alloy is not oxidized and the contact resistance can be kept lower.

According to the invention, since the contact resistance between the TFTand the drain electrode or the source electrode is decreased, rise ofthe driving voltage can be suppressed in the organic EL display deviceand, as a result, the emission efficiency of the organic EL displaydevice can be improved.

Further, in the liquid crystal display device, since the contactresistance between the TFT and the source electrode in the through-holecan be decreased, the operation speed of the driving circuit can beincreased, particularly, when the driving circuit is formed by the TFT.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross sectional view for a pixel portion of an organic ELdisplay device;

FIG. 2 is a cross sectional view in a state where a semiconductor layeris formed in a substrate in the invention;

FIG. 3 is a cross sectional view in a state where a gate electrode isformed in a substrate in the invention;

FIG. 4 is a cross sectional view in a state where an interlayerinsulation film is formed to the substrate and a through-hole is formedin the invention;

FIG. 5 is a cross sectional view showing a state where a two layeredbarrier metal is formed in the invention;

FIG. 6 is a cross sectional view showing a state where a sourceelectrode is formed in the invention;

FIG. 7 is a cross sectional view of a source electrode in the invention;

FIG. 8 is a cross sectional view in a state where a semiconductor layeris formed in a substrate in an existent example;

FIG. 9 is a cross sectional view in a state where a gate electrode isformed in the substrate of the existent example;

FIG. 10 is a cross sectional view in a state where an interlayerinsulation film is formed to the substrate and a through-hole is formedin the existent example;

FIG. 11 is a cross sectional view showing a state where a barrier metalis formed in the existent example; and

FIG. 12 is a cross sectional view showing a state where a sourceelectrode is formed in the existent example.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention is to be described for an example of applying theinvention to an organic EL display device. Before explanation of aspecific example, outline of the organic EL display device is to bedescribed. FIG. 1 is a cross sectional view for a pixel portion in theorganic EL display device to which the invention is applied. One type ofthe organic EL display device is a top emission type in which light froman organic EL layer 14 is emitted on the side opposite to the side of asubstrate 1. Another type of the organic EL display device is a bottomemission type in which light from the organic EL layer 14 is emitted onthe side of the substrate 1.

FIG. 1 is an example of the top emission type in which light is emittedin the direction of a blank arrow L. The top emission type isadvantageous in terms of screen brightness since a large emission areais available. The organic EL display device has a plurality of organiclayers sandwiched between a lower electrode 13 and an upper electrode15. The upper electrode 15 is referred to as a top anode in the casewhere the upper electrode 15 is an anode, and referred to as a topcathode in the case where the upper electrode 15 is a cathode.

Generally, the top cathode type is often used since the anode side isstable to the circumstance. That is, it is convenient to use the lowerelectrode 13 as a stable anode because, in some cases, a certainmanufacturer prepares TFT substrates including portions formed up to thelower electrode 13 and sells them another manufacturer, and anothermanufacturer forms the organic EL layer 14 and the upper electrode 15thereon.

In FIG. 1, a first underlayer 2 formed of SiN and a second underlayer 3formed of SiO₂ are deposited over a device substrate 1 formed of glass.Both the first underlayer 2 and the second underlayer 3 play a role ofpreventing impurities from the glass from contaminating thesemiconductor layer 4.

A poly-Si semiconductor layer 4 is formed on the second underlayer 3. Ana-Si semiconductor layer 4 is first formed, and converted into a poly-Sifilm by annealing the a-Si film using an excimer laser. Ion implantationand subsequent heat treatment are applied to the poly-Si therebydefining the conduction type of the semiconductor layer 4 to the p-typeor the n-type.

A gate insulation film 5 is formed over the semiconductor layer 4. Agate electrode 6 is formed on the gate insulation film 5. P or B areinjected by ion implantation using the gate electrode 6 as a mask andthen activated by a heat treatment to form a drain portion or a sourceportion of high electroconductivity to the semiconductor layer 4.

An interlayer insulation film 7 is formed on the gate electrode 6. Theinterlayer insulation film 7 plays a role of insulating the gateelectrode 6 or a gate interconnection from the video signal line or thedrain electrode and the source electrode 8 which are formed in a layerin which the video signal line extends. A through-hole is formed in theinterlayer insulation film 7 by photolithography.

Video signal lines and the drain electrode and the source electrode 8and which are formed in a layer in which the video signal line extendsare formed on the interlayer insulation film 7. Since only the sourceelectrode 8 is shown on the interlayer insulation film 7 in FIG. 1, theyare typically represented by the source electrode 8. The sourceelectrode 8 is formed of an Al alloy 82 with a large thickness in orderto decrease the electric resistance.

Al is instable and tends to diffuse into other layers. Since Aldeteriorates the characteristics of the TFT when it diffuses into thesemiconductor layer 4, a barrier metal is formed so that Al does notdiffuse into the semiconductor layer 4. As described later, theinvention has a feature of forming the barrier metal with two layers,suppressing the increase in the contact resistance between the Al alloyand the barrier metal, and decreasing the contact resistance in thethrough-hole.

Further, Al generates hillock when subjected to a heat treatment. Whenthe hillock is generated, it breaks through the insulation film to shortcircuit the source electrode 8 and the electroconduction layer of acounter electrode. In order to prevent the hillock, a cap metal 83 isformed on the Al alloy 82 to suppress the development of hillock of Al.In this example, while both the barrier metal and the cap metal 83 areformed of MoW, this is not particularly restricted and they may beformed of a high melting point metal typically represented, for example,by Mo, Ti, Ta, Mn, Ru, V, or Co, and compounds or alloys thereof.

An inorganic passivation film 9 is formed by CVD to cover the sourceelectrode 8. The inorganic passivation film 9 protects the entire TFT.An organic passivation film 10 is formed to cover the inorganicpassivation film 9, with the organic passivation film 10 also serving asa planarizing film. Since the organic passivation film 10 plays a roleof serving as a planarizing film, the organic passivation film 10 formedhas a thickness as large as about 1 to 4 μm.

To establish contact between the source electrode 8 and the lowerelectrode 13 of the organic EL layer 14, a through-hole is formed in theorganic passivation film 10 and the inorganic passivation film 9.Subsequently, an Al alloy is formed by a sputtering method or the liketo establish the contact between the lower electrode 13 of the organicEL layer 14 and the source electrode 8. Since the Al alloy has a highreflectance, the Al alloy plays a role of serving as a reflectionelectrode 12 for the top emission type.

ITO is deposited as the lower electrode 13 of the organic EL layer 14 onthe Al alloy as the reflection electrode 12. Since ITO has a large workfunction, ITO can be used as an anode for the organic EL layer 14. Afterdeposition of ITO, ITO is subjected to a heat treatment such that it hasa decreased resistivity.

The organic EL layer 14 is formed on the lower electrode 13. The organicEL layer 14 generally has a 5-layered structure comprising a holeinjection layer, a hole transport layer, an emission layer, an electrontransport layer, and an electron injection layer from the side of thelower electrode 13. IZO is deposited as a cathode on the electroninjection layer. The cathode is an upper electrode 15.

A bank 11 is formed between pixels in order to prevent destruction ofthe organic EL layer 14 caused by disconnection of step at the end. Thebank 11 may be formed of an organic material or formed of an inorganicmaterial such as SiN. When the organic material is used, the bank 11 isgenerally formed of an acrylic resin.

The emission characteristics of the organic El layer 14 are degradedwhen moisture is present. Accordingly, for the substrate 1 shown in FIG.1, the side thereof formed with the TFT and the organic El layer issealed by a sealing substrate formed of glass (not shown). The substrate1 having the organic EL layer 14, etc. formed thereover and the sealingsubstrate 1 are sealed at the periphery of them.

The present invention is configured to prevent increase in the contactresistance in the through-hole portion that establishes the contactbetween the source electrode 8 and the source portion of thesemiconductor layer 4 at the portion indicated by A. In the invention,this is true not only for the portion A but also for the contact, forexample, between the drain electrode and the drain portion of thesemiconductor layer 4 in FIG. 1.

The present invention is to be described specifically by way ofexamples.

Example 1

FIGS. 2 to 6 show a process up to the formation of the source electrode8 in the organic EL display device shown in FIG. 1. Since FIGS. 2 to 4are identical with FIGS. 8 to 10 that have been explained for theexistent example, explanation for them is to be omitted. That is, theprocess up to the state in FIG. 4 where the through-hole is formed inthe interlayer insulation film 7 and the gate insulation film 5 isidentical with that in the existent example.

Similarly to the existent example, the source electrode 8 has the threelayered structure comprising the barrier metal, the Al alloy 82, and thecap metal 83. The feature of the invention is to deposit the barriermetal film divided into two layers. That is, a lower layer 81 a of thebattier metal serves to prevent the Al atoms from diffusing into thepoly-Si semiconductor layer 4. This is a primary role as the barriermetal. An upper layer 81 b of the barrier metal serves to decrease thecontact resistance in the through-hole by enhancing the contact betweenthe upper layer 81 b of the barrier metal and the Al alloy 82. The termAl alloy 82 is used herein in the meaning of Al-containing metals.

In FIG. 5, the lower layer 81 a of the barrier metal is first formed bysputtering MoW. The thickness of the lower layer 81 a of the barriermetal is, for example, about 30 nm. Since MoW after being deposited bysputtering is in an amorphous state, MoW has an insufficient barriereffect. Then, the substrate 1 sputtered with MoW is taken out of asputtering apparatus, loaded in a heating furnace and subjected to aheat treatment to convert the MoW film into a dense film, whereby asufficient barrier effect is provided.

However, since the substrate 1 is taken out into atmospheric air in astate where MoW is deposited, the surface of MoW is oxidized. Further,while heating for the substrate 1 is performed in a nitrogen atmosphere,since oxygen remains slightly in nitrogen, oxidation of MoW alsoproceeds during heating for the substrate 1. When the Al alloy 82 isdeposited over the thus oxidized MoW, Al in the Al alloy 82 is oxidizedto form Al₂O₃. Since Al₂O₃ is an insulator, the contact resistancebetween the Al alloy 82 and MoW increases.

In the organic EL display device, if the contact resistance in thethrough-hole increases, voltage rises when a current is supplied to theorganic EL layer 14. Further, the power consumption also increases.Accordingly, the contact resistance in the through-hole should be as lowas possible.

In the present invention, after the lower layer 81 a of the barriermetal is formed of MoW and then subjected to a heat treatment such thatit has a barrier effect, the upper layer 81 b of the barrier metal isformed of MoW before formation of the Al alloy 82. The upper layer 81 bof the barrier metal is shown by a dotted line in FIG. 5. The thicknessfor MoW of the upper layer 81 b of the barrier metal is, for example, 13nm.

The upper layer 81 b of the barrier metal serves to enhance the contactwith the Al alloy 82 and, and the lower layer 81 a of the barrier metalserves to provide the barrier effect against Al. Thus the upper layer 81b does not need have a large thickness. By contrast, since it isnecessary that the lower layer 81 a of the barrier metal provide theessential barrier effect, the lower layer 81 a needs to have apredetermined thickness. That is, the lower layer 81 a of the barriermetal is formed to a thickness larger than that of the upper layer 81 bof the barrier metal.

Then, an Al alloy 82 playing a primary role of the source electrode 8 isformed by sputtering. In the invention, the Al alloy 82 is AlSi. The Alalloy 82 is formed to a thickness as large as about 250 nm to decreasethe resistance. Subsequently, MoW is formed as a cap metal 83 to athickness of about 75 nm on the Al alloy 82 by sputtering. The cap metal83 plays a role of suppressing hillock of Al. Then, a metal layercomprising the barrier metal, the Al alloy 82, and the cap metal 83 ispatterned by photolithography to form a source electrode 8, a drainelectrode, a video signal line, etc.

Since the upper layer 81 b of the barrier metal serves to enhance thecontact with the Al alloy 82 and the lower layer 81 a of the barriermetal serves to provide the barrier effect, the upper layer 81 b may bein an amorphous state as sputtered. That is, after sputtering it is notnecessary to subject the barrier metal (upper layer 81 b) to a heattreatment to form a dense film. Accordingly, the upper layer 81 b of thebarrier metal, the Al alloy 82 and, further, the cap metal 83 can beformed continuously in the chamber without breaking a vacuum state.

In the invention, the barrier metal is formed of two layers. However, asdescribed above, the upper layer 81 b of the barrier metal can besputtered continuously with the Al alloy 82 and the cap metal 83 in oneidentical vacuum chamber. Since the thickness of the upper layer 81 b ofthe barrier metal is 13 nm, the thickness of the Al alloy 82 is 250 nm,and the thickness of the cap metal 83 is 75 nm, increase in the tacttime caused by the sputtering of the upper layer 81 b of the barriermetal is extremely small. That is, the process time scarcely increaseseven when the invention is practiced.

FIG. 7 is a cross sectional view showing only the source electrode 8 inFIG. 6. In FIG. 7, the source electrode 8 comprises a barrier metal, anAl alloy 82, and a cap metal 83 in which the barrier metal is dividedinto a lower layer 81 a and an upper layer 81 b. In FIG. 7, thethickness tb1 of the lower layer 81 a of the barrier metal is 26 nm, thethickness tb2 of the upper layer 81 b of the barrier metal is 13 nm, thethickness to of the Al alloy 82 is 250 nm, and the thickness tc of thecap metal 83 is 75 nm.

In FIG. 7, since the lower layer 81 a of the barrier metal undergoes theheat treatment, a dense crystal structure is formed. By contrast, sincethe upper layer 81 b of the barrier metal is in a state as sputtered,this is in a substantially amorphous state. Further, since the crystalgrain boundary formed in the lower layer 81 a of the barrier metal isdisconnected at a portion of the dotted line B corresponding to theboundary between the lower layer 81 a and the upper layer 81 b shown inFIG. 7, the boundary can be observed, for example, by TEM and SEM.

Further, a great amount of oxygen is contained in the lower layer 81 aof the barrier metal and in the boundary between the barrier metal lowerlayer 81 a/barrier metal upper layer 81 b shown in FIG. 7, whereasoxygen is scarcely contained in the upper layer 81 b of the barriermetal and in the boundary between the barrier metal upper layer 81 b/Alalloy 82. Accordingly, by executing elemental analysis for the upperlayer 81 b and the lower layer 81 a of the barrier metal with the use ofSIMS or the like it can be confirmed that the two layers of the lowerlayer 81 a and the upper layer 81 b are formed.

The serial resistance of a plurality of through-hole portions for use inthe source electrode 8 according to the configuration of the inventionas in FIG. 7 was compared with the serial resistance of a plurality ofthrough-hole portions in which the source electrode 8 according to theexistent configuration is used. As a result, while the serial resistanceof the through-hole portions according to the configuration of theinvention was 27.8Ω, the serial resistance of the through-hole portionsaccording to the existent configuration was 112.9Ω. The serialresistance in the invention is ¼ or less of the serial resistance in theexistent example and the effect of the invention is remarkable.

Description has been made of the example of the through-hole near theTFT in the display area of the organic EL display device. In the casewhere a driving circuit is formed by a TFT at the periphery of thedisplay area, the present invention is applicable in the same manneralso to the through-hole at the periphery of the TFT of the drivingcircuit.

In the foregoing description, while the organic EL display device hasbeen explained as an example, the TFT is used also in a liquid crystaldisplay device in the same manner as in the organic EL display device.In particular, in a liquid crystal display device incorporating adriving circuit at the periphery of the display area by using a poly-SiTFT, the contact resistance in the through-hole portion gives asignificant effect on the operation speed of the driving TFT. When theinvention is applied to such a liquid crystal display device, a liquidcrystal display device incorporating a high performance driving circuitcan be attained. When the invention is applied to the driving TFT of thedriving circuit in such a liquid crystal display device, the inventionis applicable also to the switching TFT in the display area.

1. An organic EL display device comprising: scanning lines extended in a first direction and arranged in a second direction; video signal lines extended in the second direction and arranged in the first direction; and pixels each of which is formed in an area surrounded by the scanning line and the video signal line, each of the pixels having a TFT having a semiconductor layer and an organic EL layer put between a lower electrode and an upper electrode; wherein a source electrode connecting the semiconductor layer and the lower electrode is formed of three layers comprising a barrier metal, an Al-containing metal, and a cap metal, and wherein the barrier metal is formed of a first layer in contact with the semiconductor layer and a second layer in contact with the Al-containing metal.
 2. The organic EL display device according to claim 1, wherein the barrier metal and the cap metal are formed of a metal containing a high melting point metal.
 3. A liquid crystal display device comprising: scanning lines extended in a first direction and arranged in a second direction; video signal lines extended in the second direction and arranged in the first direction; and pixels each of which is formed in an area surrounded by the scanning line and the video signal line, each of the pixels including a switching TFT, a display area having a pixel electrode, and a driving TFT where a driving circuit has a semiconductor layer at the periphery of the display area; wherein a source electrode connected with the semiconductor layer of the driving TFT is formed of three layers comprising a barrier metal, an Al-containing metal and a cap metal, and wherein the barrier metal is formed of a first layer in contact with the semiconductor layer of the driving TFT and a second layer in contact with the Al-containing metal.
 4. The liquid crystal display device according to claim 3, wherein the barrier metal and the cap metal are formed of a metal comprising a high melting point metal.
 5. A method of manufacturing an organic EL display device, the device comprising: scanning lines extended in a first direction and arranged in a second direction; video signal lines extended in the second direction and arranged in the first direction; and pixels each of which is formed in an area surrounded by the scanning line and the video signal line, each of the pixels having a TFT and an organic EL layer formed over a substrate, the TFT having a semiconductor layer and the organic EL layer being put between a lower electrode and an upper electrode; wherein a source electrode connecting the semiconductor layer and the lower electrode is formed of three layers comprising a barrier metal, an Al-containing metal and a cap metal, the barrier metal is formed of a first layer in contact with the semiconductor layer and a second layer in contact with the Al-containing metal, the first layer of the barrier metal is formed by sputtering and then the substrate is heat-treated, and subsequently the second layer of the barrier metal, the Al-containing metal, and the cap metal are formed continuously over the first layer by sputtering.
 6. A method of manufacturing a liquid crystal display device, the device comprising: scanning lines extended in a first direction and arranged in a second direction; video signal lines extended in the second direction and arranged in the first direction; and pixels each of which is formed in an area surrounded by the scanning line and the video signal line, each of the pixels including a switching TFT, a display area having the pixel electrode, and a driving TFT where a driving circuit has a semiconductor layer at the periphery of the display area; wherein a source layer connected with the semiconductor layer of the driving TFT is formed of three layers comprising a barrier metal, an Al-containing metal, and a cap metal, the barrier metal is formed of a first layer in contact with the semiconductor layer of the driving TFT and a second layer in contact with the Al-containing metal, the first layer of the barrier metal is formed by sputtering and then a substrate is heat-treated, and subsequently the second layer of the barrier metal, the Al-containing metal and the cap metal are formed continuously over the first layer by sputtering. 